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http://users.isr.ist.utl.pt/~jag/courses/api1112/api1112.html

Slides 2010/2011 Prof. Paulo Jorge OliveiraRev. 2011/2012 Prof. JosGaspar

GRAFCETGRAFCET((SequentialSequential FunctionFunction ChartChart))

MEEC 2011-2012

IndustrialIndustrial AutomationAutomation(Automa(Automao de Processos Industriais)o de Processos Industriais)

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Chap. 3 PLCsProgrammingLanguages[2 weeks]...

Chap. 4 - GRAFCET (Sequential Function Chart) [1 week]TheGRAFCET norm.

Elementsof thelanguage.ModellingtechniquesusingGRAFCET.

...Chap. 5 CAD/CAM and CNC Machines[1 week]

SyllabusSyllabus::

MEEC 2011-2012

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PLCsPLCs ProgrammingProgramming LanguagesLanguages(IEC 1131(IEC 1131--3)3)

Chap. 4 - GRAFCET

Ladder Diagram

Instruction List

StructuredText

Sequential Function Chart(GRAFCET)

LD %M12AND %I1.0ANDN %I1.1OR %M10ST %Q2.0

If %I1.0 THEN%Q2.1 := TRUE

ELSE%Q2.2 := FALSE

END_IF

1

Right(1)

m

2

3

(2) b

(3) p

4

(2) a

Load

Left

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SomeSomepointerspointers toto GRAFCETsGRAFCETs((SFCsSFCs))

History: http://www.lurpa.ens-cachan.fr/grafcet/groupe/gen_g7_uk/geng7.html

Tutorial: http://asi.insa-rouen.fr/~amadisa/grafcet_homepage/tutorial/index.html

http://www-ipst.u-strasbg.fr/pat/autom/grafce_t.htm

Simulator: http://asi.insa-rouen.fr/~amadisa/grafcet_homepage/grafcet.htmlhttp://www.automationstudio.com(See projects)

Bibliography: -- Petri Netsand GRAFCET: Tools for ModellingDiscreteEvent SystemsR. David, H. Alla, New York : PRENTICE HALL Editions, 1992-- Grafcet: a powerful tool for specification of logic controllers, R. David,

IEEE Trans. on Control Systems Tech., 1995 v3n3 pp253-268[online]-- Programao de Autmatos, Mtodo GRAFCET, JosNovais,Fundao Calouste Gulbenkian-- NormeFranaiseNF C 03-190 + R1 : Diagrammefonctionnel"GRAFCET" pour la description des systmeslogiquesde commande

Homepage: http://www.lurpa.ens-cachan.fr/grafcet/

Chap. 4 - GRAFCET

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GRAFCETGRAFCET HistoryHistory

1975 Decisionof theworkgroup "Logical Systems" daAFCET (Association

FranaisedeCyberntiqueEconomiqueet Technique) on the creation of acommittee to study a standard for the representation of logical systems andautomation.

1977 GRAFCET definition(GrapheFonctionnel de CommandeEtape-Transition).

1979 Disseminationinschoolsandadoptedas researchareafor theimplementation

of solutionsof automationintheindustry.

1988 - GRAFCET becomes an international standard denominated as "SequentialFunction Chart, pela I.E.C.

Chap. 4 - GRAFCET

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Steps

1Inactive

Active 2

Initial 3

Transitions

Simple (1) R1

Fork(parallel branch)

(3) R3

J oint(parallel junction)(2) R2

J oint e fork (3) R3

Actionscan be

associated withSteps.

A logical receptivity function canbe associated with eachTransition.

GRAFCETGRAFCET Basic Elements

Connections

DirectedArc

Chap. 4 - GRAFCET

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Oriented connections (arcs)

In a GRAFCET:

An Arc can connect Steps to Transitions

An Arc can connect Transitions to Steps

A Step can have no Transitions as inputs (source);

A Step can have no Transitions as outputs (drain);

The same can occur for the Transitions.

2

1

3

(1) R1

(2) R2

4

(3) R3

Action A. .

GRAFCETGRAFCET

Chap. 4 - GRAFCET

Basic Elements

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Definition of State:

The set of markings of aGRAFCET constitutes its state.

Question:

How does the stateof a GRAFCET evolve?

2

1

3

(1) R1

(2) R2

4

(3) R3

Action A.

.

GRAFCETGRAFCET Stateof a GRAFCET

Chap. 4 - GRAFCET

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State Evolution:

Rule 5: Simultaneous activation and deactivation of a Step

In this case the activation has priority.

Rule 1: Initial State

It is characterized by the active Steps at the beginning of operation (at least one).Rule 2: Transposition of a Transition

A Transition is active or enabledonly if all the Steps at its input are active (if not it is inactive).

A Transition can only be transposed if it is active and is truethe associated condition (receptivity

function).Rule 3: Evolution of active Steps

The transposition of a Transition leads to the deactivationof all the Steps on its inputs and

the activationof all Steps on its outputs.

Rule 4: Simultaneous transposition of TransitionsAll active Transitions are transposed simultaneously.

GRAFCETGRAFCET

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Rule 2a:

All active Transitions are transposed immediately.

Rule 4:

Simultaneous active Transitions are transposed simultaneously.

1 2

(1) a

3

(2) a

4

5

(3) b

6 7

(4) b

8

9 10

(5) c

Example 1 Example 2 Example 3

. .. .

. .

..

. .

..

. .

GRAFCETGRAFCET

Chap. 4 - GRAFCET

State Evolution:

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AND Divergences:

If Step1 isactive andifa is TRUE thenStep1 isdeactivatedandSteps2 and3 are activated.

AND Convergences:

If Steps1 and2 are active andifa isTRUE thenSteps

1 and2 are deactivatedandStep3 isactivated(ifonly one of the input steps is active, the state remains).

Chap. 4 - GRAFCET

OR Divergences:

If Step 1 is active and ifa is TRUE then Step 1 isdeactivated and Step 2 is activated (state of Step 3 ismaintained).

Ifa andb are TRUE andStep1 isactive thenStep1 is

deactivatedandSteps2 and3 are activated(for any previousstateof Steps2 and3).

OR Convergences:

If Step 1 is active and ifa is TRUE then Step 1 is deactivateand Step 3 is activated (state of Step 2 remains unchanged).

The same happens for Step 2 andb.

If both Steps 1 and 2 are active andaandb are TRUEthen Steps 1 and 2 are deactivated and Step 3 is activated.

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Example:

GRAFCET stateevolution

Level activated Action. Actions can also beactivated during transitions - see next.

GRAFCETGRAFCET

Chap. 4 - GRAFCET

2

1

3

(1) R1

(2) R2

4

(3) R3

Action A

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Given4 Steps(1 to 4) and2 Transitions(t1 andt2) writea segmentof

GRAFCET to solve thefollowingproblem:

Inthe case that theSteps1 and2 are active:

if t1 isTRUE, activateStep3 (anddeactivateSteps1 and2);

if t2 isTRUE, activateStep4 (anddeactivateSteps1 and2);

otherwise, thestateismaintained.

Modellingproblem:

1

.

3 4

t2t1

2

.GRAFCETGRAFCET

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Given4 Steps(1 to 4) and2 Transitions(t1 andt2) writea segmentofGRAFCET to solve thefollowingproblem:

If Step1 isactive andt1 isTRUE

OR

If Step2 isactive andt2 isTRUE

THEN

ActivateSteps3 and4.

1

.

3 4

t2t1

2

.GRAFCETGRAFCET

Chap. 4 - GRAFCET

Other modellingproblem:

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GRAFCET state evolution, Conflicts:

There existConflictswhen the validation of a Transition depends on the same Step or whenmore than one receptivity functions can become truesimultaneously.

Solutions:

1

(1) a

2 3

(2) b

1

(1) a

2 3

(2) ba

1

(1) a b

2 3

(2) a ba b(3)

Transiction 1prioritary

Three mutualy

exclusivehypotheses

GRAFCETGRAFCET

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Example 1: modeling a control/automation system

1

Right

(1) m

2

3

(2) b

(3) p

4

(4) a

Load

Left

a b

left right

p

m load

GRAFCETGRAFCET

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Example 2: modeling a automated transport workcell

GRAFCETGRAFCET

* Conveyor A brings parts (sensor adetects part ready to lift)

* Conveyor B brings parts (sensor b detects part ready to lift)

Hanging crane, commanded withD (droit)eG (gauche),uses sensorsx, yez to detect crane over the base,over A, or over B, respectively.

Clamp of the crane grabs and releases parts with commandsPPandDP. Limit switches fppand fdp indicate grabbed andreleased part. A holding platform has two extreme positions, topand bottom, detected by switches fv+and fv-. Part release canonly be done having the holding platform up.

* Effectorpushes parts with commandsP+eP-. Limit switchesfp+and fp- indicate max and min pushing positions.

* The output conveyor is always ON.

* Conveyors A eB are commanded by other automata,independent of this workcell.

fp- fp+

fv+

fv-

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To guarantee alternating A and B, modify the program, adding thefollowing GRAFCET:

and changing the receptivity function * to:

Explanation: grab part iny, if there exists part inaand ifbhas not

the priority; ifb is true and has priority, then grab part in z.

Solution

GRAFCETGRAFCET

fp- fp+

fv+

fv-

Chap. 4 - GRAFCET

Example 2 (cont)

Note: terminology X10 of PL7 changes to S_1_10in Unity Pro

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Improvedsolution:GRAFCETGRAFCET

Chap. 4 - GRAFCET

Example 2 (cont)

a) After processing one part (P+) prepare

immediately to receive the next one: fv+.

b) Move crane (D) to an optimal waiting location(i.e. location that reduces delays): y.

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Example 3: modeling and automation of a distribution system

Objective:fill 1&2, empty 1&2refill only after both empty

Sensors:m = ON/OFFb1, h1, b2 h2 = level

Actuators:V1, V2, W1 W2 = admit/exhaust

mreservoir

b1

h1

b2

h2

V1 V2

W1 W2

GRAFCETGRAFCET

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1

(4) h2

(6) =1

5 V22 V1

(2) h1

3 W16 W2

(1) m

(5) b'2(3) b'1

4 7

(4) h2

5 V22 V1

(2) h1

3 W1 6 W2

(1) m

(5) b'2(3) b'1

4 7

GRAFCETGRAFCET

Chap. 4 - GRAFCET

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4 7

(1') m.X7 (1'') m.X4

5 V22 V1

(2) h1

3 W16 W2

(5) b'2(3) b'1

(4) h2

1

(4) h2

(6) b'1 . b'2

5 V22 V1

(2) h1

34 W1 se b167

(1) m

W2 se b2

GRAFCETGRAFCET

Chap. 4 - GRAFCET

ifif

Ch 4 GRAFCET

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GRAFCETGRAFCET

Chap. 4 - GRAFCET

Transitions can be conditions, events andconditions mixed with events

Grafcet: a powerful tool for specification of logic controllers, R. David, IEEE Trans. onControl Systems Tech., 1995 v3n3 pp253-268

(a) Eventsf andf obtained from a condition f (b) Eventa.bobtained from eventa and condition b

(c) Eventa. b obtained from eventsa and b (d) Eventa + b obtained from eventsa and b

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Properties of events (edge triggers) mixed with conditions (Boolean variables):

a =a

a . a =a, a . a = 0, a . a =a, a . a = 0

a .a =a, a .a = 0

(a . b) =a . b +b . a, (a + b) =a . b +b . a

(a . b) . (a . c) = (a . b . c)

In general, if events a and b are independent

a .b = 0

GRAFCETGRAFCET

Chap. 4 - GRAFCET

Transitions can be conditions, events andconditions mixed with events

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Macro-steps

Other auxiliary mechanisms

E10

h2

=1

5 V22 V1

h1

3 W16 W2

(1) m

b'2b'1

4 7

S8

15 V2

h2

16M10

17 V1

GRAFCETGRAFCET

Chap. 4 - GRAFCET


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Pseudo Macro-steps

Macro Actions

Force actions

Enable actions

Mask actions

GRAFCETGRAFCET

Chap. 4 - GRAFCET

Other auxiliary mechanisms


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Implementation in DOLOG80

The activity of each Step is stored in an auxiliary memory.

AM3AM4RLM1AM3

AM4RLM2

Store Rk evaluation in M100

AM1

AM2AM100SLM3AM1

AM2AM100SLM4

At startup do:AM128SLMx

...AM128SLMy(initial steps)

RLM128 43

21

(k) Rk

GRAFCETGRAFCET

Chap. 4 - GRAFCET

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Implementation in the TSX3722/TSX57

Steps

GRAFCETGRAFCET

Chap. 4 - GRAFCET


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Macro-steps

GRAFCETGRAFCET

Chap. 4 GRAFCET



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GRAFCETGRAFCET

Chap. 4 GRAFCET


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Arcs/Connectors

GRAFCETGRAFCET

Chap. 4 GRAFCET


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InformationassociatedwithStepsintheGRAFCET:

C ap G C


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S / C /

Andwhereto findinformationrelatedwithTransitions?

Does notmakesensestateoractivitynor timmings(onlynumber of occurences).

p

InformationassociatedwithStepsintheGRAFCET (bis):


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/ /

GRAFCETGRAFCETGeneral structure:

Characteristics:

p


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GRAFCETGRAFCETEditor: 8 pages

Pages0 to 7

154 cells(14*11)

Characteristics:


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GRAFCETGRAFCETOR divergences

(OR convergences)

Characteristics:


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GRAFCETGRAFCETAND divergences

(AND Convergences)

Characteristics:


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GRAFCETGRAFCETArcs/Connectors


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ANDOR

Rulesfor divergencesand convergences:


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GRAFCETGRAFCETProgrammingActions


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GRAFCETGRAFCET

Exampleof executionof Actions

Exampleof Activation/deactivation Exampleof continuousAction

ProgrammingActions


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GRAFCETGRAFCETGRAFCET Section Sctructure

LD, IL, ST

LD, IL, ST

GRAFCET


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GRAFCETGRAFCETGRAFCET Section Initialization


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GRAFCETGRAFCETGRAFCET Section Reset

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Transition sections have the following properties:Transition sections only have one single output (transition variable), whose data type is

BOOL. The name of these variables are identical to the names of the transition sections.

The transition variable can only be used once in written form.The transition variable can be read in any position within the project.Only functions can be used, function blocks or procedures cannot.Only one coil may be used in LD.

There is only one network, i.e. all functions used are linked with each other either directlyor indirectly.

Transition sections can only be used once.Transition sections belong to the SFC section in which they weredefined. If the respective

SFC section is deleted then all transition sections of this SFC section are also deletedautomatically.

Transition sections can be called exclusively from transitions.

Properties of Transition Sections (Unity Pro)

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